In the present electromagnetic drive field, the main technical means is the application of the electromagnetic induction law realized by Faraday to covert current to force or torque through the medium of magnetic field. Therefore, the output characteristics of the drive current have a strong influence on the operating characteristics of the electromagnetic drive system. Thus in ultra-high precision control field, such as voice coil motor ultra-high precision servo drive system, magnetic bearing drive system and magnetic rail suspension drive system, researchers begin to focus on the rapidity, stability and high frequency handling features of the output current of the electromagnetic drive system.
Currently in ultra-high precision electromagnetic drive field, the design for electromagnetic drive controller is mainly divided into linear power amplifier scheme and PWM power converter scheme. When the linear power amplifier scheme is adopted for the ultra-high precision electromagnetic drive control system, it has the characters as the rapid current response, the eliminated current ripple generated by switching device and the increasing stability of output current. However, if the linear power amplifier scheme is adopted, firstly, there also is current response overshoot and nonlinear region in current jump. Secondly, high performance control is more difficult due to the restricted controller design. Further, if the linear power amplifier scheme is adopted for the ultra-high precision electromagnetic drive control system, the heat generated by the system device results in large energy loss. One important development direction of the ultra-high precision electromagnetic drive control system is high overload and high acceleration, which undoubtedly impose more requirements on the power level of the components, making the linear power amplifier scheme increasingly uncapable of meeting the power requirements of the ultra-high precision electromagnetic drive control system.
If PWM power converter scheme is adopted for the ultra-high precision electromagnetic drive control system, since the control signal of the electromagnetic drive system is controlled by digital processor, the controller design of the electromagnetic drive system is more flexible, and the driving performance of the system may be controlled by more complicated control methods, at the same time, the system is featured by rapid response and high efficiency. However, there also exist certain weaknesses for the PWM power converter scheme. Firstly, since that the chopped of switching devices will inevitably generate current ripple in the system (the current fluctuations generated by the chopped of switching devices in the system are collectively referred to as current fluctuations hereinafter), the thrust (or torque) fluctuation caused by current fluctuation will greatly impact the controlling performance of the ultra-high precision electromagnetic drive control system. Secondly, the dead time set to prevent the direction connection between the upper and lower arms of the switching circuit will also lead to instability of the drive system.
Currently, in order to reduce the current fluctuation generated by PWM power converter scheme in the electromagnetic drive control system, a drive mode of high switching frequency is generally adopted. For example, the switching frequency of the switching device is raised to 200 kHz by the designer to reduce current fluctuation, and the system current fluctuation is decreased to 5% of the original fluctuation when compared with the 10 kHz switching frequency adopted in conventional electromagnetic drive control system. However, at the same time, with the switching frequency of the switching device increasing by 20 times, the switching loss of the switching device also increases by 20 times, and it is also more demanding as to the performance of switching devices, which increases the cost of the drive system. What's more, increasing the switching frequency will also increase the difficulty in the controlling of the control system and designing of the driving circuit for the drive system, substantially decreasing system stability.
As technology background, an existing electromagnetic drive control system under PWM power converter scheme is described for contrastive analysis. Refer to FIG. 1, the electromagnetic drive control system comprises an H-shaped full bridge driving circuit, including a first FET and a fourth FET connected in series constituting the left arm of the H-shaped full-bridge driving circuit, and a second FET and a third FET connected in series constituting the right arm of the H-shaped full-bridge driving circuit; a first parasitic diode is connected between the drain and the source of the first FET, a second parasitic diode is connected between the drain and the source of the second FET, a third parasitic diode is connected between the drain and the source of the third FET, a fourth parasitic diode is connected between the drain and the source of the fourth FET. It is important that the H-shaped full bridge driving circuit consists of only one DC voltage source, both sides of which are connected in parallel to the left and right arms of the H-shaped full bridge driving circuit.